PROJECT SUMMARY Hearing impairment (HI) is the most common sensory deficit in the world. Congenital HI occurs in 1-2 per 1000 newborns. Understanding the mechanism of hearing will greatly aid in the development of treatment strategies for HI. Additionally identification of pathogenic variants involved in HI is highly beneficial for genetic screening so that HI can be diagnosed early and intervention can occur at a young age to maximize the child's cognitive, social-emotional, speech and language development. The first step is to identify genes involved in the etiology of nonsyndromic (NS) HI. Although, 64 genes have been identified for autosomal recessive (AR) NSHI the vast majority of NSHI genes have yet to be uncovered. The extreme genetic heterogeneity of NSHI is due to the complex inner ear architecture where there are many different mechanisms that can cause HI. Identification of genes involved in HI is the first step in improving knowledge of the auditory process, which in turn will aid in the development of diagnostic modalities and therapeutic interventions. In order to identify new ARNSHI genes we will perform next-generation sequencing on samples from ARNSHI families from Pakistan, Hungary (Roma), Ghana, Mali and Iran and analyze the sequencing data using information on variant frequency and deleterious status and segregation of the variants with ARNSHI status within the pedigrees. We will study ~115 Pakistani, Roma, Ghanaian, Malian and Iranian families annually, to identify novel ARNSHI genes. Once a putative pathogenic variant is identified we will screen our collection of ARNSHI pedigrees to find additional families that segregate variants within the same ARNSHI gene and also request that our long-term collaborators share samples/sequence data to find additional families with pathogenic variants in the same gene. For the ~20 newly identified ARNSHI genes, expression and functional studies will also be performed to ensure gene pathogenicity as well as to elucidate a better understanding of the role the genes play in the etiology of HI.